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Task 2 - Intra-Spacesuit Radio Channel Propagation: Modeling, Measurements, and Wearable Antennas

An overview of task 2 is presented in the following video clip:

This task began in 2012 by looking at an idealized small‐scale model of the propagation

problem of human body elements within metal tubes.  Under this condition, the signal is fully contained within

 the waveguiding structure, with path losses resulting only from body absorption of the radio waves.  

We conducted a thorough literature review of related prior work that is open for public access. Our findings 

revealed that while impact of human body has been extensively studied in the context of body area networks

(BAN), there has been little work done to understand the propagation within confined setting such as a space 

suit. 

  We therefore devoted a significant amount of time understanding and developing an approximate analytic

 model for radio propagation within a space suit. A recent report by the IEEE working group on BANs 

suggested that the human body behaves more like a conductor rather than a dielectric. As a result, we

hypothesized that the coaxial cable mode of propagation would be a better analytic fit than a waveguide

 model for intra‐suit propagation.

 We used Agilent’s EM Pro simulator for our initial investigations of propagation characteristics.

 Specifically, we started with the simulation of a human arm segment within an aluminum shell

 (to mimic space suit shielding). 

 

 

emu_spacesuit

 Figure 1. EMU Space Suit Structure and the TMG insulation layers

 

Section_EMU

Figure 2. Multiple aluminized mylar in a section of EMU space suit from ILC Dover, Inc

 

image 2417

Figure 3. Researchers conducting shielding effectiveness measurements of Apollo spacesuit

Task 2 focuses on incorporating a wireless network into the space suit. First we must understand the properties of the

medium through which the signal will travel. Initially, we have come up with two deterministic models for the suit:

1) Electromagnetic cylindrical waveguide, and

2) Lossy coaxial cable.

Simulations in EM Pro were used to predict the behavior of radio signals in a space-suit environment.  Much time was dedicated

in the early stages of this task to the theory and modeling of a flesh-based conductor (i.e. a human leg) inside of a radio-opaque

sleeve, such as what would be expected as part of a space suit.  These predictions later set the stage for what measurements

would be carried out on real-life astronaut garments.

image 2413

Figure 4. Space suit insulation layers are largely radio opaque 

Our research team had the opportunity to visit the Cosmosphere in Hutchinson, KS to conduct research on retired

Apollo A7L space suits. A radio transmitter and spectrum analyzer were used to measure signal propagation through the

suit as shown above.

Following measurements on the A7L suits at the Kansas Cosmosphere, we contacted ILC Dover to obtain additional

materials for testing. These materials are used in the current EMU space suits and include modified

Thermo-Micrometeoroid Garment (TMG) metal layers.

 

Measurement of these materials confirm that the TMG layers are radio opaque as assumed in the small scale initial

propagation study work above. For large-scale testing, a graduate student in K-State's Apparel and Textiles

and Interior Design Department built a model of a modern suit using an internal Metal-fabric layer to represent

the signal propagation environment created by the TMG material.

 

construction_Spacesuit     Sleeves

Figure 5.  Construction of KSU space suit

 

Jim suit

Figure 6. Final K-State Spacesuit Mockup Model

 

Also, advancements in antenna materials research and flexibility have made it possible to integrate antennas

into flexible clothes.

  Due to congestion in existing industrial, scientific, and medical (ISM) bands, the demand to utilize

other bands is of paramount importance. Various MedRadio band antennas are investigated, evaluated, and compared,

and their shortcomings are overcome through a proposed new antenna design.  The new self-shielded folded bow-tie

antenna minimizes human body effects and maximizes off-body radio wave radiation characteristics, making

it a promising choice for the general area of WBAN technologies

as well as potential new space suit environments.